1. Field of the Invention
The present invention relates to a charge control function and a motor control circuit of a self-chargeable electronic timepiece in which a solar cell or a generator serves as a power source.
2. Description of the Prior Art
It has been heretofore desired to provide a self-chargeable electronic timepiece which comprises a primary power source such as a solar cell or a manually operated generator, and a secondary power source such as a plurality of condensers having different capacities.
Such an electronic timepiece has a condenser with a relatively large capacity which, when fully charged, is capable of driving the timepiece for several days, a condenser of a small capacity which can be instantaneously charged to produce a large voltage but which is capable of driving the timepiece for only several seconds, and a charge control circuit which connects and disconnects the primary power source to and from the secondary power source by detecting terminal voltages of both the condensers.
Operation of the charge control circuit consists of the following steps:
(a) In the initial state of charging, the primary power source is disconnected from the large capacity condenser, and an electric current is abruptly supplied only to the small capacity condenser. PA1 (b) As the terminal voltage of the small capacity condenser rises over the operation voltage of the timepiece, the primary power source is connected to the large capacity condenser, and the large capacity condenser is electrically charged. Here, the timepiece is powered only by the small capacity condenser. PA1 (c) As the terminal voltage of the small capacity condenser drops near to the minimum operation voltage of the timepiece, the primary power source is disconnected from the large capacity condenser again, and only the small capacity condenser is electrically charged. PA1 (d) Then, the large capacity condenser is electrically charged while these steps (b) and (c) are being repeated. As the terminal voltage of the large capacity condenser rises over the operation voltage of the timepiece, both condensers are connected in parallel with each other, and both the large and small capacity condensers are electrically charged in the same terminal voltage. Here, the timepiece is powered by both of the condensers. PA1 (e) As the terminal voltage of the large capacity condenser reaches near the maximum rating voltage thereof, the primary power source is short-circuited, and the charging operation is completed. PA1 (f) As the terminal voltage of the large capacity condenser decreases near to the minimum operation voltage of the timepiece, the large capacity condenser is disconnected from the small capacity condenser, and only the small capacity condenser is electrically charged. Hereafter, the steps (b) and (c) are being repeated.
The conventional self-chargeable electronic timepiece as described above has may problems as follows:
First of all, time intervals for detecting the terminal voltage are the same for the small capacity condenser and the large capacity condenser. However, it is a tendency to employ a concenser having a small capacity in order to shorten the time for initiating the oscillation. Recently, furthermore, there has been proposed a primary power source which is capable of rapidly generating electricity, such as a manually operated generator. In this case, if the voltage detecting period is long, the current supply path is not properly switched, and the small capacity condenser loses its due to the terminal voltage in excess of the maximum rating voltage or, in the worst case, the small capacity condenser is broken down.
Moreover, when a step motor is stopped by the external operation, whole circuits are in reset condition. Namely, the detection of the terminal voltage of the condenser is not carried out. Therefore, when the charge/discharge control system is stopped under charging condition, the condensers are overcharged and may be deteriorated or broken down. On the contrary, when the system is stopped under discharging, the operation may not start again even after the reset condition is released.
Furthermore, there is no means for warning the necessity of charging in the above-mentioned steps (a) and (c). Therefore, it often happens that the timepiece ceases to operate without notice to the person who carries it.
Moreover, a large number of elements are used since a plurality of voltage levels have to be detected for each condenser, and the same voltage could not be detected since different voltage-dividing impedance elements have to be used for the power sources of which the terminal voltages are to be detected.